Australia's rainforests have become the first in the world to emit more carbon than they absorb, a trend linked to climate change, a study has found.
Tropical forests are generally considered to be so-called “carbon sinks” because they absorb more emissions than they emit, with new trees offsetting the carbon emitted by dead trees.
But a study examining data from Queensland forests found extreme temperatures caused more tree deaths than tree growth.
The lead author of the study, which was published in the scientific journal Nature, said the findings have important implications for global emissions reduction targets, which are based in part on how ecosystems such as tropical forests can sequester carbon.
“Current models may overestimate the ability of tropical forests to offset fossil fuel emissions,” said Dr Hannah Karl from Western Sydney University.
The report found that with fewer new trees, trunks and branches of dead trees, known as woody biomass, became carbon emitters rather than carbon sinks about 25 years ago.
“Forests help curb the worst effects of climate change by absorbing some of the carbon dioxide released by burning fossil fuels, but our work shows this is under threat,” Dr Karl said.
Dr Karl added that the increase in the number of dying trees in recent decades has been linked to climate change, such as more extreme temperatures, a dry atmosphere and drought.
Based on 49 years of data from 20 Queensland forests, the report also found an increase in the number of cyclones, and their severity was killing more trees and making it difficult for new ones to grow.
“In this study, we have evidence that Australia's tropical rainforests are the first of their kind in the world to experience this phenomenon. [woody biomass] change,” Dr. Karl said.
“And that's really important. This could be a bit of a canary in the coal mine.”
Senior author Patrick Meir also called the results “very worrying”, telling the AFP news agency that “it is likely that all tropical forests [would] react about the same,” but added that more data and research would be needed to make a fair assessment.
Australia, one of the world's largest polluters per capita, recently announced its new carbon reduction targetspledging to cut emissions by at least 62% below 2005 levels over the next decade.
The country continues to face global criticism for its continued dependence on fossil fuels, with the government greenlighting one of the country's largest gas projects – the Woodside Northwest Shelf – continue working for another 40 years.
Last month new report on the impact of climate change found that Australia has already reached warming above 1.5°C and that no community will be immune from “cascading, worsening and simultaneous” climate risks.
